<html>
<head>
<script>

</script>
</head>
<body>
<div id="box"></div>
<script>
var box = document.getElementById("box");		// 获取盒子的引用指针
box.style.position = "absolute";				// 绝对定位
box.style.backgroundColor = "red";		// 背景色
box.style.width = w() * 0.8 + "px";	// 设置盒子宽度为窗口宽度的0.8倍
box.style.height = h() * 0.8 + "px";	// 设置盒子高度为窗口高度的0.8倍
window.onresize = function(){	// 注册resize事件处理函数，动态调整盒子大小
    box.style.width = w() * 0.8 + "px";
    box.style.height = h() * 0.8 + "px";
}
function w(){					// 获取窗口宽度
    if (window.innerWidth) 		// 兼容DOM
        return window.innerWidth;
    else if ((document.body) && (document.body.clientWidth)) 
	// 兼容IE
        return document.body.clientWidth;
}
function h(){					// 获取窗口高度
    if (window.innerHeight) 	// 兼容DOM
        return window.innerHeight;
    else if ((document.body) && (document.body.clientHeight)) 
	// 兼容IE
        return document.body.clientHeight;
}
</script>
 
</body>
</html>
